Cameras and other image capture devices often use an image sensor, such as a charge-coupled device (CCD) image sensor or a complementary metal-oxide-semiconductor (CMOS) image sensor, to capture an image. In some cases, a camera or other image capture device may use multiple image sensors, with the different image sensors having adjacent or interlaced arrays of pixels.
Many cameras and other image capture devices include one or more optical components (e.g., a lens) that are configurable to focus light received or reflected from an image on the surface of an image sensor. Before or while capturing an image, the distance between the optical component(s) and image sensor (or a tilt or other parameters of the optical components or image sensor) may be adjusted to focus an image on the image sensor. In some cases, macro (or rough) focusing may be performed for an image sensor prior to capturing an image using the image sensor (e.g., using a macro focus mechanism adjacent the image sensor). Micro (or fine) focusing is often performed after acquiring one or more images using the image sensor. Many cameras and other image capture devices perform focusing operations frequently, and in some cases before or after each image capture frame.
Focusing an image on an image sensor often entails identifying a perceptible edge between objects, or an edge defined by different colors or brightness (e.g., an edge between dark and light regions), and bringing the edge into focus. Because low light conditions tend to mute the edges in an image, focusing an image on an image sensor can be particularly difficult under low light conditions, and an optimum focus may take longer to achieve or not be possible.